Figures!

I do not have a light source for the chrono so have to do it outside and the instructions said it's best to test on a cloudy day. Yesterday it was very sunny and it was getting near the end of the day when I did the testing for the above data. Today its overcast and I was curious if I would get the same results so I repeated some of the measurements. Today I got a full 3 fps faster at both 63 lbs./315 grains and at 70 lbs./350 grains. Also, more imprtantly, the repeat measurements were much closer today with less variation. Yesterday I took an average but some readings varied by several fps and I even had some fliers that were 10 fps lower and some around 10 fps higher than the average. This lead me to believe that maybe my lighting was not sufficient since the light source is critical for this type of chronograph. Today the numbers were very consistent from one shot to the next with no fliers at all:

Alley at 27 5/8" DL at 63 lbs/315 grains with peep and loop:
296.7
296.4
296.3
296.3
296.8
296.1
296.1
above average rounded off = 296 fps (yesterday I reported 293 above)

Alley at 27 5/8" DL at 70 lbs./350 grains with peep and loop:
298.4
298.3
298.3
298.0
298.1
above average rounded off = 298 (yesterday I reported 295 above)

If you take the 298 and remove the peep it would be right at 300 or 301 and the Birth Certificate said 299 so I still feel that the data from BowTech is fairly accurate. I am not going to recalculate the effeciency numbers but the above graph may actually be a few fps on the slow side. I will check the speed over the next few days to see what type of average I get over time. I would imagine that a chrono with a light source and shot indoors would at least provide a consistent number since outdoors is subject to changing light conditions.

I should add - I also angled the chrono slightly so that the arrow was passing above at the same angle. Yesterday I think my arrow was exiting the chrono an inch or two lower than when it was entering (not parallel). Don't know if this make a difference or not but that is another change I made since yesterday.